Bistable electron device comprising axially spaced dynodes



Jan. 11, 1966 J. w. SCHWARTZ 3, 9,

BISTABLE ELECTRON DEVICE COMPRISING AXIALLY SPACED DYNODES Filed July20, 1962 2 Sheets-Sheet 1 UHF FIG 2 SOURCE 29 FIELD FORMER) L i 40/fifi/26 a OUT UT SECONDARY P B ELECTRONS 1 I ACTUATING g 3y, 54 BEAM m 2 5632 \MESH REFLECTOR r 36 24A COLLECTING ELECTRODE /DYTLODE RING INVENTORJAMES W. SCH WARTZ Jan. 11, 1966 J, w. SCHWARTZ 3,22

BISTABLE ELECTRON DEVICE COMPRISING AXIALLY SPACED DYNQDES Filed July20, 1962 I 2 Sheets-Sheet 2 29 FOCUSING UHF SlGNAL SOURCE A UTiLiZATlONDEVICE -\1T --{TlE-- s4 DELAY AND AND AND GATE GATE GATE STARTEXTINGLHSH VQLTAGE VOLTAGE.

72 p58 66 RESET sET SET INVENTOR JAMES w. SCHWARTZ F IG. 3. B

Y a A ATTORNEY United States Patent 3,223,213 BISTABLE ELECTRGN DEVICECOMPRISENG AXHALLY SPACED DYNQDES James W. Schwartz, Phoenix, Ariz.,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Navy Filed July 20, 1962, Ser. No.211,463 8 Claims. (Cl. 328255) This invention relates to flip-flops foruse in computers and more particularly relates to the use of an electronmultiplier as a flip-flop.

The prior art discloses many devices for use as flipflops in computers,such as relays, bistable vacuum-tube rnultivibrators, and bistablemagnetic cores. The various states of these devices represent bits orparts of a code character for use in the computer. The speed at whichthese flip-flops operate eventually determines the speed of thecomputer. However, the speed at which these devices can be switched fromone state to another is limited by their reactance.

One object of this invention is to provide a faster flipflop, and moreparticularly one which will operate in the millimicrosecond range.

Another object of this invention is to provide a flipflop in which thespeed of operation is dependent upon the transit time of electron beams.

A further object of this invention is to provide a memory element whichconsists of a secondary-emission electron multiplier in which amultiplication factor of unity or greater will indicate one state and amultiplication factor of less than unity another state.

In one illustrative embodiment of this invention the electron multipliercomprises a primary cathode, control electrodes, and acceleratingelectrodes for producing an electron beam; two dynodes containingcentral holes through which the electron stream passes; and a collectorelectrode between the dynodes which indicates the space charge densitytherein. The inner surfaces of the dynodes are coated with asecondary-electron emissive surface. A reflector may be used at the exitof the holes to reflect the electron stream between the two dynodes. Theelectrons which are between the dynodes, bombard the secondaryelectronemissive surfaces in response to the ultra high frequency voltageapplied to these dynodes. This bombardment creates secondary emissionwhich increases the space charge.

The electron multiplication is obtained by secondary emission. In thisprocess an electron is accelerated toward a dynode by the alternatingpotential applied to the dynode. When it strikes the dynode, it impartssuflicient energy to enable several electrons to escape. These electronsare, in turn, accelerated toward the other dynode on the second halfcycle of the alternating potential to repeat the process. in this waythe number of electrons are increased at each half cycle of thealternating voltage that is applied to the dynodes.

The low multiplication-factor state is maintained by a focusing fieldwhich causes the secondary electrons to move toward the central holes inthe dynodes. They pass through the holes and then are lost so far aselectron multiplication is concerned.

The high multiplication-factor state is maintained at a level ofmultiplication in which electrons are lost through the center holes ofthe dynodes at the same rate that secondary electrons are provided bybombardment of the dynodes. When the electron multiplier is operating ata high current, the effects of the focusing field are reduced by thehigh space charge so as to effectively increase the multiplicationfactor of the device.

In accordance with one feature of this invention, a high electronmultiplication is triggered by a low actuating cur- 3,2292% PatentedJan. 11, 1966 rent from the primary cathode, and a low multiplicationfactor is caused by an increase in this actuating current, which drivesthe core of electrons far enough so that they leave the multiplicationregion.

In accordance with another feature of this invention, the memory isswitched from one state to the other by producing bunching in theactuating beam which is in such a phase relationship with the dynodevoltages so as to spoil or to aid multiplication.

The invention and the above noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic view illustrative of one embodiment of thisinvention showing an actuating beam, a reflector for directing theelectrons into the multiplying region, two dynodes for secondaryemission purposes, a field former for urging the electrons towards thecentral holes in the dynodes, and electrodes for read out purposes;

FIG. 2 is a perspective view illustrative of another embodiment of thisinvention, in which additional holes are placed in one dynode and theelectrodes are placed opposite these holes, so that electrons spillingout of the dynode will be collected by the electrodes for read outpurposes; and

FIG. 3 is a diagrammatic view of the memory element showing the outputterminal, the set and reset terminals.

Referring now to the drawings an electron multiplier is shown with anevacuated enclosing vessel 10 as shown in FIG. 2 which may be made forexample of glass. A cathode 12 is mounted adjacent to one end of theenclosing vessel. The cathode may be of the equal-potential,indirectly-heated type, having an electron emissive surface, normal tothe longitudinal axis of the enclosing vessel It], as shown in FIG. 2.The cathode heating element is not shown. A control electrode 16 ismounted opposite the emissive surface 14 of the cathode 12. This controlelectrode contains an aperture 18 for focusing the electron beam.

Mounted opposite to the control electrode 16, in line with it and thecathode 12, is an accelerating electrode 20. This accelerating electrodecontains an aperture 22 for accelerating the beam of electrons. A fieldformer 28 is mounted opposite to the electrodes 16 and 20. This fieldformer may be a cylinder with an axis normal to the aforementionedelectrode. At each end of the field former is a dynode 24 and 26. Thesedynodes are insulated from field former 28 and are connected to a sourceof ultra high frequency voltage 29. The dynode 24 contains a centralaperture 3%! and a secondary-electron emissive surface 34; similarly,dynode 26 contains central aperture 32 and secondary-electron emissivesurface 36.

In the embodiment of FIG. 1, a mesh reflector 38 is mounted opposite theaperture 32 of the dynode 26. The collector electrode ring 40 is mountedbetween the dynodes.

In the embodiment of FIG. 2 additional apertures along the edges of thedynode 26 are shown, for example 41, 43, 44 and 46. Opposite theseapertures and out side of field former 28 are collector electrodes 48and St The embodiments of FIGS. 1 and 2 differ in the position of thecollecting electrodes and in the structure of dynode 26. In theembodiment of FIG. 1 the collecting electrode is placed between thedynodes 24 and 26; in the embodiment of FIG. 2 the collecting electrodesare placed ice on the opposite side of dynode 26 from dynode 24. In

the latter embodiment, holes 41, 43, 44 and 46 must be made in dynodes26 so that the electrons may reach the collecting electrodes 48 and 50.FIG. 1 shows the read out terminal 52, which develops a voltage in theabsence of an electron flow through from the collecting electrode ring40, through resistor 54 to voltage source 56.

The memory element may be best understood with reference to FIG. 1. Whenthe memory element is in the state, there is no output voltage onterminal 52. This is because the space between the dynodes 24 and 26contains an electron cloud, which provides a source of current from theelectron collector 40 through resistor 54 to the positive terminal ofvoltage source 54. This drops the voltage from 56 across the resistor 54and drives the voltage of terminal 52 toward 0.

When the memory element is in the 1 state a voltage appears at terminal52. This is because there are no electrons between the dynodes 24 and26. The circuit containing voltage source 56, resistor 52 and electroncollector 40 is effectively open-circuited. The voltage at the positiveterminal of voltage source 56 appears at terminal 52 since the currentthrough resistor 54 is negligible.

Assume first that the memory element is in the 1 state, that is, thereare no secondary electrons between the dynodes and therefore a constantoutput voltage appears at terminal 52. To switch the memory element fromthe 1 state to the 0 state an actuating beam must be introduced ataperture 30. This beam, which may originate in a beam selection sectionsuch as selectron geometry will supply the space charge forces andinitiating electrons to go from this vacant space to the multiplyingstate in which secondary electrons are present between the dynodes.

The electrons which have been supplied by the actuating beam areaccelerated first towards dynode A and then towards dynode B by theultra high frequency voltage source connected to these dynodes. Whenthese electrons strike the secondary-electron emissive coating 34 and 36on the dynodes 24 and 26 more electrons are driven off. This fieldformer 28 focuses the electron towards the center hole in the dynodes.Then the secondary electrons which are driven off of the dynodes areequal to the electrons that are lost through the center holes in thedynodes due to the focusing field, an equilibrium state is reached. Thisequilibrium is reached because, when a large cur-rent exists in thedevice, the space charge forces spoil the 0- cusing for the electronsnear the edge of the core in the memory element so that they do not passthrough the hole, thus increasing the number of electrons between thedynodes. The electrons between the dynodes are attached to thecollecting electrode ring 40. These electrons cause a current to flowthrough resistor 54 to the source of voltage 56. The voltage drop acrossresistor 54 drives the terminal 52 to ground to indicate the 0 state ofthe memory device.

Reversion to the vacant state is also produced by the actuating beam.One way of doing this is to drive the multiplying core of electrons farenough that they completely pass outside of the multiplying region. Theelectric field created by the increased actuating beam drives thesecondary electrons beyond the edges of the dynodes and away from thecentral holes so that they are lost for electron multiplicationpurposes.

. Another means of reverting to the vacant state is to produce bunchingin the actuating beam which is in such a phase relationship with thedynode voltages as to spoil multiplication. The electrons are bunched insuch a way as to create the greatest electric field due to the bunchedelectron at the cross-over point of the ultra high frequency voltageapplied to the dynodes. This will provide the maximum displacement awayfrom the central holes towards the edges of the dynodes to the secondaryelectrons since at that point they have the greatest travel time underthe influence of the electric field from the actuating current. Thisreduces the number of secondary electrons available to strike the nextdynode and create further secondary electron emission. Also, theelectric field will counteract the UHF field during one half of eachcycle and thus slow down the speed of electrons.

When the memory element has reverted to its vacant state and noelectrons are made available to the collecting electrode ring, thecurrent through resistor 54 ceases and the voltage at terminal 52 isdriven to the 1 state.

The embodiment of FIG. 2 operates in substantially the same manner asthe embodiment of FIG. 1. However, the dynode 26 contains further holes41, 43, 44 and 46, which are used for read out purposes. When the memoryelement is in its multilpying state electrons will spill out of theseholes. The collecting elements 48 and 59 for read out purposes areopposite these holes and will attract electrons in the same manner asthe collecting electrode ring 40 collected the electrons in theembodiment of FIG. 1.

The control and accelerating grids 16 and 20 shown in FIG. 2 may be usedto produce the bunching and actuating beam which is necessary to returnthe memory element to the vacant or 0 state. To accomplish this, theaccelerating electrode must be modulated by the ultra high frequencyvoltage source of the same frequency as that used to modulate thedynodes 24 and 26. This modulation will create a velocity modulatedbeam, in that the electrons will pass through the electrodes during thepositive cycle will be accelerated and those that pass through duringthe negative cycle will be retarded. Consequently, the faster movingelectrons of the beam will catch up with the slower moving electronsthus causing an in creased electron density in the beam. This variationin the density of the beam of the electrons is called bunching. To spoilthe multiplication of the memory element, the bunches of electronsshould pass across the aperture 30 at the time that the ultra highfrequency voltage begins to accelerate the electrons which have beenemitted from the secondary-electron emission surface of dynode 24towards the opposite dynode. This will cause the maximum deflection ofthese electrons away from the multiplication region of the dynode. Thephase of this bunching is controlled by the distance from the modulatedelectrodes to the aperture 30. If the electrodes 16 and 20 are used forthe purpose of bunching electrons, the beam must be provided by anotherelectron accelerator for the electron gun.

The number of secondary electrons emitted per primary electron dependsupon the velocity of the primary bombarding electrons, the nature of thematerial, the condition of its surface and the potential conditionssurrounding the bombarded surface. For typical surfaces of barium oxidewith a primary voltage of 400 volts, the

ratio of secondary electrons to primary electrons will be approximately4.5.

A common secondary-electron emission coating consists of a thin film ofcesium on an intermediate film of cesium oxide covering a silverelectrode. The secondary emission from this surface approachesmilliamperes per watt of incident primary-electron energy. As the energyof the primary electrons is increased the secondaryernission ratioincreases to a maximum and then gradually decreases.

FIG. 3 shows a noncomplementary embodiment of the invention. When theset terminal 58 is pulsed AND gate 60 is opened to pass an extinguishingvoltage from voltage source 62. This voltage is applied to acceleratingelectrode 20 which increases the electron stream from electron gun 12through aperture 30 of dynode 24.

If the memory element is in its 0 state, there is an electron cloudbetween the dynodes 24 and 26. This cloud results from themultiplication of electrons by secondary emission. The electrons arecollected by collector electrodes 48 and 50 and cause a current to fiowthrough resistor 54, to drive the voltage at 52 to zero.

The extinguishing voltage 62 which appears at electrode 20 acceleratesthe electrons from electron gun 12 causing a high current to flowthrough the apertures 30 and 32 of the dynodes. This current drives thesecondary electrons to the edges of the dynodes and beyond thesecondary-electron emissive surface, where they are lost for electronmultiplying purposes.

Since no electrons can be collected by electrodes 48 and 50, no currentflows through resistor 54 and therefore terminal 52 rises to thepositive voltage of source 64 to indicate the 1 state of the memoryelement.

This 1 state can also be obtained by pulsing terminal 66. This will openAND gate 68 to the UHF voltage from source 29. This voltage is appliedthrough the AND gate to electrode 20 to modulate the electron beam fromelectron gun 12. The delay 76 is adjusted to provide the proper phase inthe modulating volt-age such that the electron beam is bunched so as tospoil multiplication. This will interrupt the current from battery 64and cause terminal 52 to register a l.

A pulse at reset terminal 72 opens AND gate 74 to voltage source 76,which appears on grid 20. The voltage from source 7s is less than thatfrom voltage source 62. The electron beam, controlled by this voltage,provides the initiating electrons for the secondary emission process.The electric field created by the electron current through the apertures39 and 32 in the dynodes must not be so strong as to tangentiallyaccelerate the secondary electrons to a sufficient degree as to forcethem beyond the edges of the dynodes.

This initiating voltage will start the secondary-electron emission toswitch the memory element into its electron multiplying state. Theinitiating electrons from electron gun 12 and newly released secondaryelectrons will be forced back and forth to bombard dynodes 24 and 26under the influence of the UHF source 29. This bom bardment will, inturn, cause further secondary-electron emission until an equilibriumstate is reached in which the newly created secondary electrons equalthe elec trons lost through the apertures 3i? and 32 in the dynodes.

In this state an electron cloud is present between the dynodes. Theelectrons are collected by electrodes 48 and St) to provide an electronflow through resistor 54 to voltage source 64. This current causes avoltage drop across resistor 54 and drives the terminal 52 to the 0state.

The embodiment of FIG. 3 is that of a noncomplementing ffip-flop.However, it is clear that conventional steering gates can be used toconvert this embodiment to that of a complementing flip-flop.

The above embodiments can be used as memory elements which wi l operatein the millimicrosecond range. These elements may be used for fastacting random access or cyclic access computers.

It is important to realize that the beams used in this device are notrequired to alter the potential of any electrode but only to alter thefree space potential. Hence, there are no capacitive lags involved andthe only time limit to the speed of the device is that of the transittime of the electrons. For spacings of a few thousandths of an inch anddynode voltages in the order of a hundred volts, a transit time of lessthen one tenth of a millimicrosecond are involved. The secondaryemission process itself takes less then one one-hundredth of amillimicrosecond. The basic element is capable of either essentiallycontinuous readout or an interrogated type of readout requiring a periodappreciably less than one millimicrosecond.

Control of the state of the binary element is readily achieved by meansof a control electron beam which enters the multiplication region andalters the electrostatic fields therein. Beam deflection techniques suchas used in traveling wave oscilloscopes may be useful in directing orsteering control and/ or interrogating beams. Similarly klystron typebeam bunching techniques may also be applied. The bandwidth andoperating frequency of either of these devices is high enough to providesubnanosecond operation.

It is apparent that the basic element is capable of power gain. Thisimmediately suggests the direct coupling of elements to perform controland logic functions. The coupling would, of course, be by means ofelectron beams emanating from individual multiplier cells and going toone or more other cells. Each cell can control not only the presence orabsence of a beam of secondary electron origination but one or morebeams from a static or DC. flood source.

A complete computer consisting of appropriately intercoupled layers ofmany cells could be contained in a small volume. Obviously multipletraversals of a logic sequence through the layers of the computer can beeffected by beam reflection or bending procedure beyond the outsidesurfaces of the multilayered array.

While there has been described what is at present considered thepreferred embodiment of the invention it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein Without departing from the invention and it is therefore aimedin the appended claims to cover all such changes in modifica tion thatmay fall within the scope of the invention.

What is claimed is:

1. A flip-flop, having a first state with an electron multiplicationfactor of less than unity and a second state with an electronmultiplication factor of more than unity, comprising:

a source of a beam of electrons;

a plurality of axially spaced dynodes positioned in the path of saidbeam of electrons containing holes through which electrons may pass;

an alternating voltage source connected to said dynodes, wherebyelectron in the space between said dynodes are alternately acceleratedfirst toward one dynode and then toward another dynode to causeincreased secondary emission such that the increase in elec trons due tosecondary emission from said dynodes will be greater than the loss ofelectrons through said holes when said flip-flop is in said second stateand less than the loss of electrons through said holes when saidflip-flop i in said first state; and

means for initiating and terminating the secondary emission action ofsaid dynodes whereby said flipfiop may be switched from said first statehaving an electron multiplication factor of less than unity to saidsecond state having an electron multiplication factor of more thanunity.

2. A flip-flop, in accordance with claim 1, including mean providing afocusing field which causes said secondary electrons to move toward atleast one of said holes in said dynodes.

3. A flip-flop, in accordance with claim 2, in which at least one ofsaid dynodes has a secondary-electron emissive surface.

4. A flip-flop, in accordance with claim 3, in which said alternatingvoltage source is characterized by an UHF signal.

5. A flip-flop, in accordance with claim 2, in which an electroncollector is mounted between said dynodes whereby said collector isnonconductive when said flip-flop is in said first state and saidcollector is conductive when said flip-flop is in said second state.

6. A flip-flop, in accordance with claim 2, in which one of said dynodescontains at least one additional hole through which electrons may passfor subsequent computer operation purposes.

7. A flip-fiop, in accordance with claim 4, in which said source ofelectrons comprises:

(a) a beam selection section; and

(b) a reflector mounted in the path of the beam.

8. A millimicrosecond flip-flop, having a first state with an electronmultiplication factor of less than unity and a second state with anelectron multiplication factor of more than unity, comprising:

(a) a plurality of axially spaced dynodes;

7 8 (b) at least one of said dynodes having a secondary- (g) meansresponsive to the electron density between electron ernissive surface;said dynodes for controlling further electronic corn- (c) an UHF voltagesource connected to said dynodes; ponents. (d) a source of primaryelectrons; (e) means for forming said primary electrons into a 5Refemmes fitted y the Examiner (S i l f 1 t l d f d b UNITED STATESPATENTS con ro means or a terna e y irec ing sai earn of electronsbetween said dynodes with such a veloc- 2026892 1/1936 Hemtz 328 642,071,515 2/1937 Farnsworth 32824 3 X ity and phase as to cause them tobe multlplled by 2 639 12/1941 Honmqnn 328 277 secondary emission whendnven against said second- 10 2,726,328 12/1955 clogston 328 255 Xary-electron emissive surface by said UHF voltage source and fordirecting said beam of electrons be- GEORGE N WESTBY Primary Examinertween said dynodes with such a velocity and a phase as to cause them tospoil secondary emission multi- ROBERT SEGAL, Examinerplication; and v15

1. A FLIP-FLOP, HAVING A FIRST STATE WITH AN ELECTRON MULTIPLICATIONFACTOR OF LESS THAN UNITY AND A SECOND STATE WITH AN ELECTRONMULTIPLICATION FACTOR OF MORE THAN UNITY, COMPRISING: A SOURCE OF A BEAMOF ELECTRONS; A PLURALITY OF AXIALLY SPACED DYNODES POSITIONED IN THEPATH OF SAID BEAM OF ELECTRONS CONTAINING HOLES THROUGH WHICH ELECTRONSMAY PASS; AN ALTERNATING VOLTAGE SOURCE CONNECTED TO SAID DYNODES,WHEREBY ELECTRONS IN THE SPACE BETWEEN SAID DYNODES ARE ALTERNATELYACCELERATED FIRST TOWARD ONE DYNODE AND THEN TOWARD ANOTHER DYNODE TOCAUSE INCREASED SECONDARY EMISSION SUCH THAT THE INCREASE IN ELECTRONSDUE TO SECONDARY EMISSION FROM SAID DYNODES WILL BE GREATER THAN THELOSS OF ELECTRONS THROUGH SAID HOLES WHEN SAID FLIP-FLOP IS IN SAIDSECOND STATE AND LESS THAN THE LOSS OF ELECTRONS THROUGH SAID HOLES WHENSAID FLIP-FLOP IS IN SAID FIRST STATE; AND MEANS FOR INITIATING ANDTERMINATING THE SECONDARY EMISSION ACTION OF SAID DYNODES WHEREBY SAIDFLIPFLOP MAY BE SWITCHED FROM SAID FIRST STATE HAVING AN ELECTRONMULTIPLICATION FACTOR OF LESS THAN UNITY TO SAID SECOND STATE HAVING ANELECTRON MULTIPLICATION FACTOR OF MORE THAN UNITY.